Due to the audio device changes implemented when Windows performs the upgrade to version 10 from your existing Windows installation, users may find that their audio devices/sound appear to have stopped working with Bria 4. Bria 4 has simply lost its association with the audio device(s) you were using due to the changes in the upgrade, and the fix is a simple device settings adjustment in Bria 4.
Please go the Bria 4 menu and then navigate as follows: Softphone -> Preferences -> Devices. Once you are in this section, you should see that the devices selected are set to "none" in the Headset mode, Speakerphone Mode, and Other Devices tabs. Your original devices you were using prior to the Windows upgrade should be available for selection under all three of these tabs in the devices menu. Please set the devices correctly for your situation in all three categories.
Once you have tried the device setting changes mentioned, please test a call with Bria 4. You should find that functionality is restored to how it was prior to the upgrade to Windows 10. If you are still having issues with sound or devices after trying this procedure, please open a ticket and post a screenshot of your device settings so that we can review them and provide additional troubleshooting steps.